MFA issue for a user error 500121

Question

We have a user that her MFA stuck and keep getting error : 500121 .

I have reset the user's MFA several time and set it up again . the user MFA account is setup correctly

When she try to access an external site that require MFA then she got 2 choices , getting MFA code , In spite of i have added the user phone number but never get choice to choose sms text when the site asking for authentication . This error found on the user azure profile :

Authentication requirement

Multifactor authentication

Status

Failure

Continuous access evaluation

No

Sign-in error code

500121

Failure reason

Authentication failed during strong authentication request.

Additional Details

The user didn't complete the MFA prompt. They may have decided not to authenticate, timed out while doing other work, or has an issue with their authentication setup.

I have reset the MFA , re-installed MFA App , QR scan works fine and codes generates fine . Notifications is enabled but she never got notification.

Any idea ? and the user is not locked in MFA ( in Azure ).

Br

Sam